1. Field of the Invention:
The present invention relates to a powdered rubber composition.
2. Description of the Background:
In recent years an increasing number of publications have appeared which are concerned with the utilization of powdered rubbers. These publications also show methods of producing the powdered rubbers.
The reason for the increasing widespread interest in powdered rubbers is easily found in the present situation of the state of rubber processing technology. However, the rubber processing techniques presently used all are encumbered by the high costs of time, energy, and personnel. The main reason for these high costs is the state of the rubber raw material which is available in bale form.
The mastication of the rubber bale, and the intimate mixing of the masticated rubber with fillers, mineral oil plasticizers, and vulcanization accelerators are carried out on rollers or in kneaders. To avoid quality reductions, the mixtures are prepared in several steps. The mixture is generally stored between steps. Extruder-pelletizers or extruder-roller dies generally follow the kneaders or rollers.
Only a completely new processing technology can lead the way out of this extremely unsatisfactory and costly technique of rubber processing. For this reason, the use of pourable powdered rubber has been discussed and tested during recent years, because it provides the possibility of being able to process rubber mixtures simply and rapidly, like thermoplastic powders.
Several methods of producing powdered, pourable rubber-filler mixtures, especially rubber-carbon black mixtures based on general-purpose rubbers, have already been found and described such as in German Pat. Nos. 21 35 266 and 24 39 237; German Patent Exposition, No. 22 14 121; German Patent Application Disclosures Nos. 22 60 340, 23 24 009, 23 25 550, 23 32 796, and 26 54 358. An important aspect of the processes described in these disclosures is the use of special surface-active compounds in the preparation of the powdered rubber. Since the main objective of using powdered rubbers, as already stated, is to increase the economy in the area of rubber processing, a basic prerequisite for the success of these efforts is the economical production of rubbers in powdered form.
A process that points in this direction is described and claimed in German Pat. No. 28 22 148. An important drawback of this state of the art process is the fact that not only are powders produced with particles of various sizes, but the powdered particles have a relatively higher content of filler with decreasing particle size. This can result in problems during processing which appear in the form of segregations. The consequences are that the molded parts exhibit variable filler contents as a result of being prepared from the powdered rubbers. This drawback has meanwhile been eliminated by a more recent process modification. However, the process does not solve the problem of controlling the particle size of powdered rubbers. Specifically, the particle size, on the one hand, is very important in the production of the powders (dewatering, drying), and on the other hand, during the processing (oil absorption, pourability, absence of dust). A need has therefore continued to exist for a method of preparing a pourable, powdered rubber of improved properties.